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ABSTRACT Plainfin midshipman fish (Porichthys notatus) exhibit seasonal auditory plasticity that enhances their reproductive success. During the summer, type I male midshipman acoustically court females and both the males and females exhibit increased auditory sensitivity during this period. The enhanced auditory sensitivity is associated with increased density of sensory hair cells in the saccule but not the utricle, suggesting that different mechanisms underlie physiological plasticity in distinct inner ear regions. To better understand how shifts in hair cell number occur within auditory tissues, we examined cell turnover across breeding states and sexes in midshipman fish. We found that reproductive type I males exhibited less saccular cell proliferation than non-reproductive males without a change in cell death, indicating a net loss of saccular cells during the breeding season. By contrast, saccular cell proliferation increased in summer females, with no seasonal changes in other inner ear epithelia. Collectively, our data reveal that multiple mechanisms are likely to contribute to seasonal auditory plasticity within a single species, potentially within the ear of an individual animal. 

Most of us have heard birds sing during the spring breeding season. Did you know that some fish also sing to attract mates? We study plainfin midshipman fish, a fascinating fish that makes its home along the Pacific Coast of North America. The big male fish sing during the summer months and their sound-producing muscles get bigger in the summer, probably to make them sound more attractive to females. Female midshipman fish go through seasonal changes, too. In the summer their hearing improves, which helps them pick the right male to mate with. We study hearing in female plainfin midshipman, measuring how their ears respond to sound and how the number of hearing cells in their ears changes between winter and summer. We want to know how seasonal changes in hormones affect hearing in this “songbird of the sea”.